Slide valves utilized in controlling high temperature and high velocity flow of products through the valve have a number of disadvantages--for example, require seat plates and seat plate bolting, have seat plate distortion, and the utilization of bolting that is under load due to differential pressure in the valves and are only as strong as the bolting system strength of bolts resulting in seat plate distortion, do not have a positive seal against bypass from differential pressure, do not allow for proper alignment of the orifice plate, and do not provide for future expansion of the port opening.